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Bloom period has been long for tree fruit growing in east Michigan. Recent cold temperatures were very close to causing flower bud damage for some growers.

Weather

The roller coaster ride of widely fluctuating temperatures continued this past week. Cold temperatures in the low 30s on Sunday and Monday mornings, May 15-16, were very close to causing damage to flower buds. Frost fans were running at most farms and strawberry growers had long periods of irrigation for frost control, especially on Monday morning. It appears we dodged the bullet on this latest cold event. Many growers received soft, mushy hail in storms over the weekend. It does not appear we had any damage to flower buds.

Our season has dropped back to slightly behind normal in terms of crop stages of our fruit crops, and just about normal in terms of growing degree-day (GDD) totals. Based on the 10-day forecast, it appears we will move ahead rapidly over this time period.

Most of our region has experienced three to six days with measurable precipitation over the last week, bringing well over an inch of precipitation for most growers. Our soils generally have good moisture supplies at this time.

Tree fruits

Apples remain mostly at full bloom to very early petal fall for growers south of the I-69 corridor and king bloom to full bloom to the north, with the exception of growers close to Lakes Erie and Huron, where fruit growth is delayed. This has been the longest bloom period I can remember for apples and other tree fruits. There is not the usual spread of bloom time from the south to the north this season.

Honey bees, bumble bees and native pollinators have been very active during the several windows with warmer temperatures. This will make thinning especially challenging this season. With warmer temperatures predicted for later this week, it appears that a good thinning window may be opening.

Some growers are seeing apple tree death, mostly in lower lying area of blocks. This is due to cold damage on trees that were not fully hardened during the severe cold temperatures in the winters of 2014 and 2015. Affected trees generally have sections of bark on the trunk or lower scaffold branches with a scruffy or flaky appearance. These trees will most likely die over this or next season. This delayed winter injury will continue to show up for several years.

Powdery mildew was the only new disease to be found in apples in the last week, and only at a few farms. There is a slight curl or upwards roll in the expanding leaves as well as a few spots on the upper leaf surface. This leaf curling is not to be confused with the Roundup injury I am also starting to see, more details below.

Most of our Michigan State University Enviro-weather stations had between one and four wetting events over this past week, with many ending up with two apple scab infection periods. At my apple scab spore trapping location, I caught apple scab spores, but the numbers are declining as primary apple scab season is working its way to the end. I caught 145 spores on the spore rods in a brief rain shower Monday evening, May 16. Most growers have applied one or two fungicide covers this past week to control apple scab. Many apple growers have noted the past few days that the apple scab model on the MSU Enviro-weather website states that all of the spores have been discharged, thus thinking we are at the end of primary apple scab season. This is not the case in the real world, as I am still catching spores at my trapping location. Remember that the model is just that, a model, not the real world of apple production.

Fire blight infection has not been an issue at most farms this past week, despite the many rain events. The exception here is for growers who had hail. With bloom still present, growers need to be on guard as epiphytic infection potential (EIP) numbers on the MSU Enviro-weather website are creeping up toward the end of the week. Growers should watch blocks and varieties where fire blight was a problem last season, as well as be on the lookout for oozing fire blight cankers where it was a problem last season.

I am starting to see apple limbs with small, strap-like leaves where Roundup was applied last season to the herbicide strip beneath the tree, and some landed on a limb. MSU Extension advises growers that now is the time to make spot applications of selective herbicides to control Canada thistle. Herbicides such as Stinger, Spur or the newer Starane Ultra have been effective in controlling Canada thistle.

Pears are mostly 5 to 10 millimeters in diameter, with a few blooms still open. Pear psylla adults continue flying.

Peaches are at shuck split for growers in the south and in the shuck for most others to the north. Oriental fruit moth trap catch continues being seen at many farms, with some also at biofix. Most growers have a good crop of peaches this season.

Sweet cherries still have a few blooms open, but most are 4 to 6 millimeters in diameter. Tarnished plant bugs are a new pest to report in sweet cherries. For growers at shuck split, insect controls will be going on soon. Brown rot control sprays continue being made.

Tart cherries are mostly at petal fall to being in the shuck.

Plums are in the shuck for European types and Japanese types are mostly at shuck split, however some Japanese varieties have little to no crop this season.

Small fruits

Grapes are at bud burst to 1 inch of shoot growth for Concord types and mostly at late bud burst for European varieties.

Strawberries remainedat 20 percent bloom for most farms, as bloom has been in a holding period this past week. Flower trusses and new leaves continue emerging from the crown. Most strawberry growers have frost-protected a least once in the last week. Strawberry clipper or clipped buds have been seen at several farms in the last few days, as have spittle bugs at a few farms. Angular leaf spot, another new disease for the week, has also been found on leaves at a few farms.

Raspberry shoots and leaves continue emerging for summer fruiting types, with 2 to 3 inches of new shoot growth. Flower buds continue emerging on summer raspberries. New canes continue emerging from the ground in fall raspberries; the longest canes are 4-8 inches in length.

Blueberries are at full bloom for early varieties with most varieties at early bloom. I have not found any signs of mummy berry mummies on the ground this season.

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